Controller in a vehicle

ABSTRACT

A control unit in a vehicle is provided in which power is supplied via a converter that provides an electrical isolation. For the data exchange with external components and other components in the control unit that are not electrically isolated, the component isolated by this electrical isolation is additionally connected to a coupling element that likewise provides an electrical isolation.

FIELD OF THE INVENTION

The present invention relates to a control unit in a vehicle.

SUMMARY

An example control unit in a motor vehicle in accordance with thepresent invention may have the advantage that, due to the decoupling ofrelevant components in a control unit, especially an airbag controlunit, from the vehicle electrical system, cases of a fault such as ashort circuit of the minus output stage of the ignition circuit controlto the vehicle ground or a short circuit of the plus output stage to thevehicle ground can lead to an unintentional triggering of restraintdevices. This is due to the fact that, in such a case of a fault in thecontrol unit according to the present invention, no unintended currentcan flow via the firing element, i.e., a firing pellet for example.

It may be particularly advantageous that the resistance value between aprinted circuit board ground in the control unit and the vehicle groundis not critical, which may be especially important in vehicles that havean aluminum chassis, which feature higher resistance values due to thetype of construction. Moreover, in the case of this material, due to thesignificant oxide layer formation, it is difficult to guarantee, for theentire service life of the vehicle, the very low-impedance connectionwhich may be necessary without the present invention.

Furthermore, due to the electrical isolation in the ICs, which aresupplied by the electrically isolated supply voltage, it is possible toretain the cost-effective 40 V manufacturing processes even at highelectrical system voltages, in the case of a 42 V electrical system forinstance. Hence, it is not necessary to switch to more expensiveprocesses with higher voltages, since the vehicle electrical system hasno relationship to internal supply voltages. Here, especially in thecase of the ignition IC, i.e., the ignition circuit control, space maybe saved in the case of the output stage transistors since these nolonger need to be short circuit-proof vis-à-vis the high electricalsystem voltage. It is furthermore advantageous that, due to theelectrical isolation, in the case of a fault of a short circuit of theplus output stage to the vehicle ground, the firing pellet can continueto be fired in the standard triggering case since the voltage at theplus output stage is no longer short-circuited.

It may be particularly advantageous if the electrical isolation in theconverter used for supplying power to the control unit is achieved by atransformer, in particular, a DC/AC voltage converter on the primaryside and a rectifier on the secondary side. Since the battery in thevehicle supplies a direct current, the DC/AC voltage converter isnecessary to transmit the power via the transformer. A rectifier isprovided on the secondary side because the components situated in thecontrol unit on the secondary side require a DC voltage. The DC/ACvoltage converter can take the form of an oscillator or a chopper.

In addition, it may be advantageous if the coupling element used fortransmitting data from external peripheral components to the controlunit electronics or to the ignition circuit control takes the form of anoptocoupler, so that the electrical isolation in the transmission ofdata is ensured here as well.

Moreover, it may be advantageous if the converter is connected to atleast one energy store, preferably a capacitor, which, in the event of adisconnection of the power supply, i.e., of the vehicle battery,continues to run the converter and does so for a specified time. Thisguarantees a short-term operation of the airbag control unit especiallyin an accident situation.

Either the entire control unit electronics, i.e., in particular theprocessor, or merely the ignition circuit control may be provided as thecomponents in the control unit protected by the electrical isolation.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the present invention are depicted in thefigures and are explained in greater detail below.

FIG. 1 shows a first exemplary embodiment of the present invention.

FIG. 2 shows a second exemplary embodiment of the present invention.

FIG. 3 shows a block diagram of the converter.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

In conventional airbag control units, the ground connection to thecontrol unit supply is established either via a separate ground line orvia a conductive connection of the printed circuit board ground to themetal control unit housing which is conductively connected to thevehicle ground. In both methods, a connection of the lowest possibleimpedance is required to avoid different potentials of the printedcircuit board ground relative to the vehicle ground. For this purpose,especially the resistance of the separate ground line or the contactresistance of the metal control unit housing to the vehicle ground mustbe taken into account.

If there is no case of a fault, i.e., if there is no short circuit ofthe minus output stage to the vehicle ground, no short circuit of theplus output stage to the vehicle ground or an interruption of theconnection to the vehicle ground, this will result in the followingswitching-on operation:

When closing the ignition lock switch, the starting current of theairbag control unit is limited by the resistances of the supply line andpre-fuse of the series resistance on the printed circuit board forlimiting the charging current and the resistance of the separate groundline or the contact resistance of the metal control unit housing to thevehicle ground. The charging current flows, typically at 220 to 470 μF,to an electrolytic capacitor, which is required for filtering the supplyvoltage. In addition, a diode is provided as a reverse-polarityprotection diode. Depending on the battery voltage and the totalresistance of the resistances just mentioned, the charging current is ofa magnitude of a multiple of 10 A. This current flows through thecontact resistance or the resistance of the separate ground line andthere causes a voltage drop so that a voltage rise of the printedcircuit board ground vis-à-vis the vehicle ground can occur. Thisvoltage rise is normally not critical.

If there is a short circuit of the minus output stage of the ignitioncircuit control to the vehicle ground, however, then the printed circuitboard ground will be raised positively as just described. Thus, due tothe fault in the minus output stage, the firing pellet is directlyconnected to the vehicle ground. As a result, the vehicle ground has amore negative potential than the printed circuit board ground. If thepotential difference is sufficiently high, parasitic diodes on theignition circuit IC become conductive, and a current flows through thefiring pellet. The duration of the current flow and the current levelare possibly great enough to cause an unintended triggering.

If, however, there is a short circuit of the plus output stage to thevehicle ground, the firing pellet will be connected to the vehicleground when it is connected to the plus output stage. For this reason aswell, the vehicle ground has a more negative potential than the printedcircuit board ground. If the potential difference is sufficiently high,the diodes on the IC for the ignition circuit control become conductive,and a current flows through the firing pellet. The duration of thecurrent flow and the current level are possibly great enough to cause anunintended triggering.

Now if there is an interruption of the connection to the vehicle groundand a short circuit of the minus output stage to the vehicle ground or ashort circuit of the plus output stage to the vehicle ground, then thefollowing situation results:

The starting current is no longer able to flow through the connection tothe vehicle ground, since the control unit has no ground connection. Itflows in this case through the parasitic diodes on the ignition circuitIC. In addition, a current flows through the firing pellet. The durationof the current flow and the current level are in any event great enoughto cause an unintended triggering. The control unit in this case obtainsthe ground connection via the firing pellet.

According to the present invention, a control unit is now proposed whichin the case of these faults does not result in an unintentionaltriggering of the firing pellet. Particularly due to the electricalisolation, the current flow, which can result in an unintentionaltriggering of the firing pellet, is not possible.

The electrical isolation is necessary to isolate the control unitvoltage supply from the vehicle electrical system. This is preferablyachieved using a transformer in a DC voltage converter. To this end, ageneration of AC voltage is required on the primary side and a rectifieron the secondary side. In addition, signals of the external peripheralequipment, e.g., a diagnostic line or a belt-buckle switch or sensorsthat relate to the ground of the vehicle electrical system, must beconnected to the electrically isolated components in the control unitvia so-called coupling elements. Optocouplers are preferably used assuch coupling elements. These coupling elements can be designed asdiscrete elements or can also be integrated in an appropriate IC of thecontrol unit.

FIG. 1 shows a first block diagram of an example device according to thepresent invention. An ignition lock switch 1 isolates a vehicle battery2, which is connected on the other side to ground, namely to the vehicleground, at chassis 3. On the other side, ignition lock switch 1 isconnected to a converter 5 located in a control unit 4. Converter 5 ison the one side connected to vehicle ground 3 and on the other side toan internal ground 7. Converter 5 itself has an electrical isolation, sothat vehicle ground 3 is isolated from internal ground 7 in terms ofdirect current. Converter 5 provides the supply voltages 8 to a controlunit electronics 6. Control unit electronics 6 conducts a data exchange9 with the coupling elements 10, which are likewise located in controlunit 4. Coupling elements 10—which themselves also feature an electricalisolation, since optocouplers are preferably used here—are connected onthe other side to external peripheral equipment 11 via a datainput/output 12. External peripheral equipment 11 is in turn connectedto vehicle ground 3. External peripheral equipment 11 means sensorsand/or diagnostic lines and/or belt-buckle switches.

Converter 5 here is a DC voltage converter. This DC voltage converternow has a configuration as represented in FIG. 3. There a DC/AC voltageconverter 20 is provided, which is connected to a transformer 21. Arectifier 22 is provided on the secondary side of transformer 21. DC/ACvoltage converter 20 may take the form of an oscillator or, for example,also of a chopper. This is then used to generate an AC voltage that canbe transmitted via transformer 21. Rectifier 22 then again rectifies theAC voltage, so that control unit electronics 6 can be supplied.Rectifier 22 can in particular take the form of a bridge rectifier,having diodes connected in the arms of the bridge. However, simpler oralternative rectifier circuits are also possible.

FIG. 2 shows a second embodiment of the present invention. Identicalcomponents as in FIG. 1 are indicated by the same reference numerals.Again, an ignition lock switch 1 is connected to a vehicle battery 2,which in turn is connected to a vehicle ground 3. On the other side,ignition lock switch 1 is connected to the control unit 4 and thereby toa converter 13 having an electrical isolation and a converter 18 havingno electrical isolation. Converter 13 is designed as shown in FIG. 3. Onthe other side, converter 13 is connected to the internal ground 15 ofcontrol unit 4 and provides the supply voltages to an ignition circuitIC 16 via a line 14. Via a data input/output, ignition circuit IC 16 isconnected to coupling elements 10, which carry out a signal exchangewith the control unit electronics 17. Control unit electronics 17receives the power supply from converter 18 without electricalisolation, and control unit electronics 17 is further connected tovehicle ground 3. In addition, the control unit electronics is connectedvia a line 19 to the external peripheral equipment 11, which itself inturn is related to vehicle ground 3.

This example shows that the electrical isolation according to thepresent invention with the aid of a converter can also be used merely toisolate individual components in the control unit that are critical withregard to safety, while leaving other components connected to thevehicle ground.

It is also possible to isolate other components or additional componentswhich, in the case of a fault, can likewise lead to the fatalconsequences presented at the beginning of the description. As shownabove, however, the electrical isolation also has the advantage that itallows for a voltage conversion which makes it possible to continue touse existing manufacturing processes for the components of the controlunit.

Using a power reserve capacitor as an energy store, converter 5 or 13can continue to be operated for a defined self-sufficiency period evenwhen the battery, i.e. the power supply, is disconnected.

1-8. (canceled)
 9. A control unit in a vehicle, comprising: a converterhaving an electrical isolation for supplying power to at least onecomponent; at least one coupling element having an electrical isolationand connectable to the at least one component, the coupling elementbeing used for data transmission; and a ground connection assigned tothe at least one component.
 10. The control unit as recited in claim 9,wherein the converter includes a transformer for electrical isolation, aDC/AC voltage converter being provided on a primary side, and arectifier being provided on a secondary side.
 11. The control unit asrecited in claim 10, wherein the DC/AC voltage converter includes anoscillator.
 12. The control unit as recited in claim 10, wherein theDC/AC voltage converter includes a chopper.
 13. The control unit asrecited in claim 9, wherein the at least one coupling element is anoptocoupler.
 14. The control unit as recited in claim 9, wherein theconverter is connected to at least one energy store which runs theconverter in case a power supply is disconnected.
 15. The control unitas recited in claim 9, wherein the at least one component is an ignitioncircuit control for a restraint device.
 16. The control unit as recitedin claim 9, wherein the at least one component is electronics of thecontrol unit.